Cooling system

ABSTRACT

A system for cooling telecommunications device includes an air inducing mechanism which pushes air into an enclosure of the device and an air exhaust mechanism which exhausts the air from the enclosure. The rate at which the air is pushed into the enclosure is less than the rate at which the air is expelled from the enclosure and these two rates are controlled such that the pressure differential between the pressure within the enclosure and the ambient pressure outside the enclosure is minimized. By minimizing this pressure drop, the airflow mechanisms are able to operate more efficiently, that is, they are able to operate at substantially near their design speed.

RELATED APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/254,091, filed on Dec. 8, 2000. The entire teachingsof the above application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] To protect telecommunications devices, such as computers, fromextreme temperatures, cooling systems are used to maintain a desiredtemperature inside enclosures housing the electronic components of thedevices. For example, conventional air apertures, such as openings inthe enclosures, are employed to facilitate the circulation of air aboutthe electronic components. Fans can also be used with the apertures,either integrated within or mounted to the enclosure, to exhaust airfrom the enclosure after the air has circulated about the electroniccomponents.

SUMMARY OF THE INVENTION

[0003] Typically, conventional air apertures operate inefficiently. Forinstance, there may be an air filter covering the aperture that becomesblocked up with dust over time. In some devices, the energy release bythe components is large enough to require the use of fans. Fans thatonly exhaust air from an enclosure or only push air into the enclosureoperate inefficiently because of the large pressure differential betweenthe pressure within the enclosure and the ambient pressure outside theenclosure.

[0004] The present invention implements a system for coolingtelecommunications devices. Specifically, in one aspect of theinvention, the cooling system includes an air inducing mechanism whichpushes air into an enclosure of the device, and an air exhaust mechanismwhich exhausts the air from the enclosure. The rate at which the air ispushed into the enclosure is less than the rate at which the air isexpelled from the enclosure and the two rates are optimized such thatthe pressure differential between the pressure within the enclosure andthe ambient pressure outside the enclosure is minimized. By minimizingthis pressure drop, the airflow mechanisms are able to operate moreefficiently, that is, they are able to operate at substantially neartheir design speed.

[0005] Embodiments of this aspect can include one or more of thefollowing features. The airflow mechanisms can be fans. There can be twofans mounted adjacent to each other for pushing air into the enclosure,and there can be two fans also mounted adjacent to each other forexpelling the air from the enclosure. Each fan module may be removable,such that when one fan fails it may be removed while the other fanscontinue to operate to prevent thermal damage of the components withinthe enclosure. Each fan module, along with any replacement fan module,can be placed in the enclosure interchangeably, without modification, inany of the four locations. All of the fan modules are keyed or polarizedto the full extent so as not to adversely affect the air flow directionor the performance of the heat transfer capabilities of the systemwithin the enclosure.

[0006] In other embodiments of this aspect, the system can include acontroller for variably controlling the speed of the airflow mechanismsor operating the airflow mechanism at a preset speed. The first airflowmechanism can be mounted in a lower half portion of the enclosure, whilethe second airflow mechanism is mounted in an upper half portion of theenclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

[0008]FIG. 1 is an isometric view of an enclosure for atelecommunications product with a cooling system in accordance with anembodiment of the present invention.

[0009]FIG. 2a is an exploded perspective view of a fan module of thecooling system of FIG. 1.

[0010]FIG. 2b is a view of a connector cable of the fan module of FIG.2a.

[0011]FIG. 3a is an isometric view of a panel of the housing of FIG. 1in which the module of FIG. 2 is mounted.

[0012]FIG. 3b is an exploded isometric view of the panel of FIG. 3a.

[0013]FIG. 4 is a block diagram of a control system for the coolingsystem of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0014] A description of preferred embodiments of the invention follows.Referring to FIG. 1, there is illustrated a system for cooling atelecommunications enclosure. As shown in FIG. 1, an enclosure 10 houseselectronic components (not shown) within the enclosure and includes arear mounting panel 12 in which four fan modules 14 a, 14 b, 14 c, and14 d, collectively referred to as modules 14, are mounted. Enclosure 10includes a front casing 11 that is provided with keying tabs 13 toensure a proper fit between the front casing 11 and the rear mountingpanel 12.

[0015] Referring now to FIG. 2a, each fan module 14 includes a frontplate 30 and a back encasing 32 which encase a fan assembly 33. The fanmodule 14 also includes a front handle 34 and a back handle 36 which canbe grabbed by an operator to assist in placing and removing the modulefor the mounting panel 12 of the enclosure 10. The back housing 32 isprovided with a set of keying tabs 38 which fit into a set of slots 39of the front plate 30. The front plate 30, the back housing 32 and thefan assembly 33 are held together by a set of screws 40. The front plate30 and the back housing 32 are provided with respective screenedopenings 42 and 44. These openings have diameters of approximately thesame size as a circular opening 45 of the fan assembly 33. The fanassembly 33 holds a set of fan blades and a motor 48. A power cable 50(FIG. 2b) extends from each fan module 14 and includes a connector 52which plugs into a connector housing 54 located inside the enclosure 10.The connector 52 has two screws 56 attached to the connector housing 54,used for attaching the connector 52 to the inside of the enclosure 10.

[0016] Referring also to FIGS. 3a and 3 b, the rear mounting panel 12 isprovided with a set of keying stubs 60 which engage with a set of keyingholes 62 of the front plate 30 of the fan module 14. These stubs 60provide the keying and orientation for each fan module 14 as they relate(mount) to the rear panel 12. Since all the fan modules 14 areidentical, the top fan modules 14 c and 14 d can only go into the rearpanel 12 in one direction and the bottom fan modules 14 a and 14 b canonly be mounted in the opposite direction as allowed by the stubs 60.This prevents placing the fan modules in the wrong locations. The rearmounting panel 12 is also provided with a set of keying slots 64 whichengage with the keying tabs 13 of the front casing 11. Each fan module14, as well as any replacement fan module, can be placed in theenclosure 10 without modifying the module in any of the four locationsof the rear panel 12. Thus the fan modules 14 are fully interchangeable.The fan modules 14 are keyed, or polarized, to ensure that they areproperly oriented in the rear panel 12 so as not to adversely affect theair flow direction through the enclosure 10 or the performance of theheat transfer capabilities of the cooling system.

[0017] Although the front plate 30 and the back housing 32 of the fanmodule 14 are typically made of metal, they can be made from plastics.The stubs 60 are made of metal for durability.

[0018] In use, fan modules 14 a and 14 b push air into the enclosure, asindicated by arrow 20. The air circulates about the components insidethe enclosure thereby cooling the components. Fan modules 14 c and 14 dexhaust air from the enclosure in the direction as shown by arrow 22. Inthe present embodiment, the fan modules operate at a predefined speed.For example, modules 14 a and 14 b each operate at approximately 240cubic feet per minute (CFM), while each of modules 14 c and 14 d aredesigned to operate at about 300 CFM. The upper modules 14 c and 14 dmust operate at a higher speed because of the thermal expansion of theair as it is heated while flowing about the heat generating components.Note, the push (modules 14 a and 14 b)/pull (modules 14 c and 14 d)arrangement of the configuration shown in the drawings. If the uppermodules operate alone, the pressure differential between that within theenclosure and the ambient outer pressure is larger than when thesemodules operate in series with the lower modules 14 a and 14 b. Inessence, the “pushing” of the air by modules 14 a and 14 b lowers thesystem impedance of the air flow through the enclosure. By doing so,both the upper and lower fan modules are able to operate moreefficiently.

[0019] When a fan module fails, the module can easily be removed fromthe rear mounting panel 12. The system is designed such that the fansthat have not failed continue to operate at their predefined speed whilethe failed fan is replaced. Even in such circumstances, the system isable to adequately cool the electronic components within the enclosureto prevent thermal damage to the components.

[0020] To properly choose fans that able to dissipate the generated heatwithin the enclosure, the heat generated must be approximated and thesystem impedance must be calculated.

[0021] The major sources of resistance within the enclosure include theresistance of the channels between the boards, the boards themselves,and the openings for the air into and out of the board chassis. In thepresent example, the dimensions of the board channels are as follows:height, H, is about 18 inches, width, W, is about 1.11 inches, and thedepth, D, is about 15 inches.

[0022] The resistance of the board channels is calculated to be${R\quad b\quad c} = {\frac{3.1 \times 10^{- 4} \times H}{\left( {W \times D} \right)^{2}} = {\frac{3.1 \times 10^{- 4} \times 18}{\left( {1.11 \times 15} \right)^{2}} = {20.13 \times 10^{- 6}}}}$

[0023] in units of$\frac{{{in} \cdot H_{2}}O}{\left( \frac{{ft}^{3}}{\min} \right)^{2}}$

[0024] The total resistance of the boards in the systems is calculatedto be${Rboards} = {\left( \frac{1}{\frac{14}{\sqrt{R\quad b\quad c}}} \right)^{2} = {\left( \frac{1}{\frac{14}{\sqrt{20.13 \times 10^{- 6}}}} \right)^{2} = {0.109 \times 10^{- 6}}}}$

[0025] And the resistance of the slots are found to be${Rslot} = {\frac{2.4 \times 10^{- 3}}{{Af}^{\quad 2}} = {\frac{2.4 \times 10^{- 3}}{\left( {18 \times 15 \times 0.5} \right)^{2}} = {0.132 \times 10^{- 6}}}}$

[0026] where Af is the open cross sectional area of a slot, with 50% ofthe cross section open. The total system impedance is then

Rsystem=Rslot+Rboards=2×0.132×10⁻⁶+0.106×10⁻⁶

[0027] thus,

Rsystem=0.373×10⁻⁶

[0028] The heat generated, W, within the enclosure 10 in the presentexample is approximately 2000 Watts, and the airflow, Q (in units ofCFM), needed to dissipate that heat is$Q = {\frac{W}{c_{p}{\rho\Delta}\quad T} = {\frac{1.76 \times W}{\Delta \quad T} = {\frac{1.76 \times 2000\quad {Watts}}{15{^\circ}\quad {C.}} = {235C\quad F\quad M}}}}$

[0029] where c_(p) is the specific heat of air at sea level, p is thedensity of air at sea level, and ΔT is the maximum allowable temperaturerise in the system, which is about 15° C.

[0030] With the estimated airflow and system impedance calculated above,the pressure loss in the system can be calculated from the relation

Psystem=Rsystem×Q ²=0.373×10⁻⁶×235²=0.021

[0031] in units of in. H₂O. Thus with a 235 CFM requirement across apressure of 0.021 in H₂O, appropriate fans were selected based on theirstatic pressure curves.

[0032] In the embodiment discussed above, a controller coupled to thefans operates the fans at a preset speed. However, in alternativeembodiments of the system, as illustrated in FIG. 4, amicroprocessor-based controller 70 in conjunction with a temperaturesensor 72, such as a thermistor, detects high temperature conditions andvaries the speed of the fans 14 to accommodate higher temperatures. Whenabnormally high temperatures are detected, for example, when one fanfails, the other fans operate at their maximum speed. The fans may alsodefault to a maximum speed when the controller fails or when thecontroller is removed from the device for replacement.

[0033] Both the intake and exhaust fans can use 48 volts of DC nominaloperating voltage. The fan module can also provide a tachometer output,which is referenced to a negative lead supply and produces two pulsesper revolution. There can be a programmable speed control, whichprovides variable speed operation by pulse width modulation. The fanspeed can be proportional to the duty cycle present on the fan input.Maximum speed is obtained when the lead is open and it drops down to aminimum speed when the lead connects to the negative lead of the fansupply voltage.

[0034] While this invention has been particularly shown and describedwith references to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. An apparatus for cooling a telecommunicationsdevice, comprising: a first airflow mechanism mounted in an enclosure ofthe device and oriented within the enclosure to induce air into theenclosure; and a second airflow mechanism mounted in the enclosure ofthe device and oriented for expelling air out of the enclosure; whereina rate at which the air is induced into the enclosure is less than arate at which the air is expelled, and the induced rate and the exhaustrate are controlled to minimize the pressure differential between apressure within the enclosure and an ambient pressure outside theenclosure.
 2. The apparatus of claim 1, wherein the first airflowmechanism is a first fan, and the second airflow mechanism is a secondfan.
 3. The apparatus of claim 2, further comprising two additionalfans, the third fan being mounted adjacent to the first fan and orientedto induce air into the enclosure, and the fourth fan being mountedadjacent to the third fan and oriented to exhaust air from theenclosure.
 4. The apparatus of claim 3, wherein each fan is removable.5. The apparatus of claim 4, wherein when one fan fails, the other fansoperate at a sufficient speed to prevent thermal damage to thecomponents within the enclosure.
 6. The apparatus of claim 1, whereinthe first airflow mechanism and the second airflow mechanism areinterchangeable modules.
 7. The apparatus of claim 6, wherein themodules are keyed to ensure the proper orientation of the modules whenmounted in the enclosure so that the airflow direction through theenclosure is not adversely affected.
 8. The apparatus of claim 1,further comprising a controller which controls the speed of the firstairflow mechanism and the second airflow mechanism.
 9. The apparatus ofclaim 8, wherein the controller is programmable such that the speedcontrol of each mechanism is variable.
 10. The apparatus of claim 8,wherein the controller operates the first airflow mechanism and thesecond airflow mechanism at preset speeds.
 11. The apparatus of claim 1,wherein the first airflow mechanism is mounted in a lower half portionof the enclosure.
 12. The apparatus of claim 1, wherein the secondairflow mechanism is mounted in an upper half portion of the enclosure.13. The apparatus of claim 1, wherein the first airflow mechanism andthe second airflow mechanism are removable from the enclosure.
 14. Theapparatus of claim 1, wherein the first airflow mechanism operates inseries with the second airflow mechanism.
 15. The apparatus of claim 1,wherein the first airflow mechanism and the second airflow mechanism arecontrolled to operate at preset speeds.
 16. The apparatus of claim 1,wherein the first airflow mechanism and the second airflow mechanism arecontrolled to operate at variable speeds.
 17. A method for cooling antelecommunications device, comprising the steps of: inducing air into anenclosure of the device with a first airflow mechanism; expelling airout of the device with a second airflow mechanism; and and operating thefirst air flow mechanism and the second airflow mechanism such that arate a which the air is induced into the enclosure and a rate at whichthe air is expelled are controlled to minimize the pressure differentialbetween a pressure within the enclosure and an ambient pressure outsidethe enclosure.
 18. The method of claim 17, further comprising the stepof variably controlling the speed of the first airflow mechanism and thespeed of the second airflow mechanism.
 19. The method of claim 17,further comprising the step of controlling the first airflow mechanismand the second airflow mechanism to operate at preset speeds.